The present invention relates to a method and a device for preventing the formation of streaks in the weft of the cloth when a textile loom is restarted after a stoppage.
Each time a loom is stopped for any reason (breakage of threads, momentary slackening of the feed tension, etc.) defects known as weft "streaks" in the cloth may be produced when the loom is restarted.
These streaks are more likely and more noticeable the longer the loom is stopped. The defects are also more marked when the yarn used in the weaving is of the type which is almost without resilience and likely to fail under tension. With such yarns, even a brief stoppage of the loom is sufficient to cause an extension of the cloth as well as of the yarn, with the consequent displacement of the beating-up line of the weft. In effect, when a stoppage of the loom occurs, the boundary between the cloth and the warp is displaced generally, as a result of the extension of the yarn, from the nominal position in which the sley of the loom beats the weft. According to the type of yarn used and the characteristics of the loom, the weaving line may be dispaced towards the warp beam or towards the cloth beam. In the first case, a weft streak of the type known as "overbeating" is formed in the fabric when the loom restarts: the first weft inserted when weaving restarts is too near the last weft inserted before the stoppage. This defect is perceptible visually as a thickening, almost a superposition, of the weft threads in the cloth.
In the second case, a streak of the type known as a "gap" is formed in the cloth when the loom restarts: the first weft inserted after restarting is too far from the last weft inserted before the stoppage.
In both cases, the piece of cloth produced has a defect which inevitably affects its market value.
Various devices for resolving the problems described above have been proposed. Thus, for example, the Italian patent application 68110-A/82, in the name of the same Applicant, proposed devices for detecting the size and direction of the displacement of the boundary between the warp and the cloth during a stoppage of the loom and for repositioning this boundary correctly immediately before weaving recommenced.
In European patent application No. 0184779, also in the name of the same Applicant, however, a system is proposed in which, immediately before the loom is restarted, the warp is rewound by an amount predetermined on the basis of the characteristics of the yarn, the loom and the duration of the stoppage, in order to compensate for the extension of the warp which has occurred during the stoppage.
The known devices produced hitherto and described above tend to remedy the problems stated above by attempting to compensate for their effects rather than by eliminating their cause.